Homo

Especially since the 2010s, the delineation of Homo in Australopithecus has become more contentious. Traditionally, the advent of Homo has been taken to coincide with the first use of stone tools (the Oldowan industry), and thus by definition with the beginning of the Lower Palaeolithic. But in 2010, evidence was presented that seems to attribute the use of stone tools to Australopithecus afarensis around 3.3 million years ago, close to a million years before the first appearance of Homo.[37] LD 350-1, a fossil mandible fragment dated to 2.8 Mya, discovered in 2013 in Afar, Ethiopia, was described as combining "primitive traits seen in early Australopithecus with derived morphology observed in later Homo.[38] Some authors would push the development of Homo close to or even past 3 Mya.[f] Others have voiced doubt as to whether Homo habilis should be included in Homo, proposing an origin of Homo with Homo erectus at roughly 1.9 Mya instead.[39]

The most salient physiological development between the earlier australopithecine species and Homo is the increase in endocranial volume (ECV), from about 460 cm3 (28 cu in) in A. garhi to 660 cm3 (40 cu in) in H. habilis and further to 760 cm3 (46 cu in) in H. erectus, 1,250 cm3 (76 cu in) in H. heidelbergensis and up to 1,760 cm3 (107 cu in) in H. neanderthalensis. However, a steady rise in cranial capacity is observed already in Autralopithecina and does not terminate after the emergence of Homo, so that it does not serve as an objective criterion to define the emergence of the genus.[40]

Homo habilis[edit]

Homo habilis emerged about 2.1 Mya. Already before 2010, there were suggestions that H. habilis should not be placed in genus Homo but rather in Australopithecus.[41][42] The main reason to include H. habilis in Homo, its undisputed tool use, has become obsolete with the discovery of Australopithecus tool use at least a million years before H. habilis.[37] Furthermore, H. habilis was long thought to be the ancestor of the more gracile Homo ergaster (Homo erectus). In 2007, it was discovered that H. habilis and H. erectus coexisted for a considerable time, suggesting that H. erectus is not immediately derived from H. habilis but instead from a common ancestor.[43] With the publication of Dmanisi skull 5 in 2013, it has become less certain that Asian H. erectus is a descendant of African H. ergaster which was in turn derived from H. habilis. Instead, H. ergaster and H. erectus appear to be variants of the same species, which may have originated in either Africa or Asia[44] and widely dispersed throughout Eurasia (including Europe, Indonesia, China) by 0.5 Mya.[45]

Homo erectus[edit]

Homo erectus has often been assumed to have developed anagenetically from Homo habilis from about 2 million years ago. This scenario was strengthened with the discovery of Homo erectus georgicus, early specimens of H. erectus found in the Caucasus, which seemed to exhibit transitional traits with H. habilis. As the earliest evidence for H. erectus was found outside of Africa, it was considered plausible that H. erectus developed in Eurasia and then migrated back to Africa. Based on fossils from the Koobi Fora Formation, east of Lake Turkana in Kenya, Spoor et al. (2007) argued that H. habilis may have survived beyond the emergence of H. erectus, so that the evolution of H. erectus would not have been anagenetically, and H. erectus would have existed alongside H. habilis for about half a million years (1.9 to 1.4 million years ago), during the early Calabrian.[43]

A separate South African species Homo gautengensis has been postulated as contemporary with Homo erectus in 2010.[46]

A taxonomy of Homo within the great apes is assessed as follows, with Paranthropus and Homo emerging within Australopithecus (shown here cladistically granting Paranthropus, Kenyanthropus, and Homo).[a][b][6][47][4][5][48][49][50][51][52][53][54][excessive citations] The exact phylogeny within Australopithecus is still highly controversial. Approximate radiation dates of daughter clades are shown in millions of years ago (Mya).[51] Graecopithecus, Sahelanthropus, Orrorin, possibly sisters to Australopithecus, are not shown here. Note that the naming of groupings is sometimes muddled as often certain groupings are presumed before any cladistic analysis is performed.[49]